Risk and reliability
The aim of the Risk and ReliabilityGroupis to develop and implement novel statistical methods to support risk and reliability management of underwater systems. We focus on providing training within the Natural Environment Research Council (NERC) on how to apply these methods.
We work with all branches of the NERC Ocean Technology and Engineering Group (OTEG) and with the NERC Marine Systems department. Our applications are autonomous underwater vehicles (AUVs) – including gliders, moorings and marine sensors.
Risk management process tailored to AUV operations
We have developed a Risk Management Process for AUVs that is based on targeted reliability. An accepted risk is defined by the AUV owner. This acceptable risk converts into a reliability target that must be met by the AUV operators. We have developed extensions to existing statistical survival methods that allow us to assess the risk of loss for an AUV undertaking a mission in a defined environment, under sea ice, for example.
Availability management
One of the most important requirements for AUV operation is to know the probability of the vehicle being ready for deployment when required; this is denoted as the vehicle’s availability. We develop Markov chains, a graphical probabilistic model, of the AUV deployment to predict AUV availability. The approach has also been applied to other marine sensors.
Expert judgment elicitation
Risk assessment is based largely on expert subjective judgment. Over the years, we have been applying and tailoring formal expert judgment elicitation processes to the underwater technology development community. We have conducted numerous expert judgment elicitation exercises.
Reliability testing
Most of our equipment is deployed in extreme conditions. When these conditions can be recreated in the lab, we work with OTEG engineers to devise reliability testing plans for mechatronics (intelligent machine) components and software modules.
Incident/Accident investigation
As a part of our programme we offer a no-fee service to those in the NERC marine science community with a risk or reliability problem or incident. Our aim is to help owners and operators establish the root cause, or the most likely cause or causes, without the attribution of blame. We can call upon our own experience in risk analysis and management, and also the engineering expertise in the Underwater Systems Laboratory (USL).
Useful references
1. Griffiths, G. et al. On the reliability of the Autosub Autonomous Underwater Vehicle. Underwater Technology 25(4), 175–184 (2003).
2. Griffiths, G. & Trembanis, A. Towards a risk management process for Autonomous Underwater Vehicles. Pp. 103–118 in: Griffiths, G. & Collins, K., Proceedings of a Masterclass on AUV Technology for Polar Science. SUT, London (2007). ISBN 0 906940 486
2. Griffiths, G. & Trembanis, A. Eliciting expert judgement for the probability of AUV loss in contrasting operational environments (in Proceedings 15th International Symposium on Unmanned Untethered Submersible Technology, 2007).
3. Griffiths, G. & Brito, M. P. AUV risk analysis and management. Proc. UUVS, Southampton (2009).
4. Brito, M. P., Griffiths, G. & Challenor, P. G. Risk analysis of Autonomous Underwater Vehicle operations in extreme environments: Expert judgment elicitation, aggregation and survival modelling. Risk Analysis (2010). DOI: 10.1111/j.1539-6924.2010.01476.x
5. Brito, M. P. and Griffiths, G. (2009). A Bayesian approach to predicting risk of loss during Autonomous Underwater Vehicle missions. Submitted to IEEE J. Oceanic Eng.
6. Brito, M. P & Griffiths, G. A Markov chain state transition approach to establishing critical phases for AUV reliability. IEEE J. Oceanic Eng. (2010). DOI: 10.1109/JOE.2010.2083070
7. Brito, M. P. & Griffiths, G. Analysis of robustness of statistical survival estimates via multiple objective optimization (in Proc. PSAM, Seattle, June 2010).
8. Brito, M. P. & Griffiths, G. Results of expert judgments on the faults and risks with Autosub3 and an analysis of its campaign to Pine Island Bay, Antarctica, 2009. Proc UUST 2009 (New Hampshire, 2009).
9. Griffiths, G. & Brito, M. P. Reliability of two REMUS-100 AUVs based on fault log analysis and elicited expert judgment. Proc. UUST 2009 (New Hampshire, 2009).
10. Collins, K. & Griffiths, G. (eds) 2008 AUV Science in Extreme Environments. Society for Underwater Technology (London, 2008). ISBN 0 906940 50 8.
11. Brito, M. P., Griffiths, G. & Trembranis, A. Eliciting expert judgment on the probability of Loss of an AUV operating in four environments. Southampton, UK, NOCS. (NOCS Research and Consultancy Report, 48, 2008).
12. Lampitt, R. et al. Brito, M. P. Reliability Case Notes No. 2. PAP 2007: DOMS mooring loss report. Southampton, UK, NOCS. (NOCS Research and Consultancy Report, 51, 2008).
13. Furlong, M. E. & Brito, M. P. Reliability Case Notes No. 4: Autosub6000 and Autosub3 actuator potentiometer failure analysis and testing report. Southampton, UK, NOCS. (NOCS Research and Consultancy Report, 58, 2009).
